Precision, reliability, and long life in machine tool spindles don’t happen by accident. One of the most important—but often overlooked—factors is bearing preload.
Preload is the controlled axial force applied to bearings during spindle assembly. It’s not just a step in installation—it’s a key design decision that directly affects how your spindle performs every day.
What Does Proper Preload Do?
When done right, bearing preload delivers real-world benefits:
1.Higher Rigidity = Better Accuracy
Preload removes internal clearance, so the bearing resists deflection under cutting forces. This means your spindle stays stable during heavy cuts—resulting in tighter tolerances and smoother surface finishes.
2.Less Runout, Less Vibration
With no play between components, rotational accuracy improves. Axial and radial runout drop, reducing chatter and vibration—critical for fine-detail machining.
3.Longer Bearing Life
Even load distribution prevents stress hotspots. Plus, preload reduces skidding (micro-slippage) of rolling elements—especially at startup or high speeds—cutting down on wear and early failure.
4.Quieter, Smoother Operation
A well-preloaded bearing runs smoothly without the clunk or noise caused by parts moving in and out of clearance zones. Quiet operation often signals a healthy spindle.
5.Stable Performance Under Heat
During high-speed runs, metal parts expand. Proper preload compensates for thermal growth, keeping bearings securely seated and preventing loss of precision.
How to Apply Preload the Right Way
Getting preload right isn’t guesswork. Here’s what matters:
Choose the Right Amount
Too little? Your spindle lacks stiffness.
Too much? Bearings overheat and fail fast.
The ideal preload is usually 10–30% of the bearing’s original radial clearance, adjusted for your specific speed, load, and temperature conditions. When in doubt, consult a bearing specialist.
Pick the Best Method for Your Application
1.Fixed (Position) Preload: Uses precision-ground spacers. Best for medium-speed, high-load spindles where maximum rigidity is needed.
2.Spring (Constant Pressure) Preload: Uses disc or coil springs. Ideal for high-speed spindles—it automatically adjusts for thermal expansion and wear, avoiding dangerous over-preload.
Account for Heat in Real Operation
In high-precision machines, temperature changes affect preload. Advanced spindles may include sensors and active systems to maintain optimal preload during operation—keeping accuracy consistent from first cut to last.
Final Thought: Preload Is Part of the System
Great spindle performance comes from more than just high-quality bearings—it comes from how they’re installed and tuned. For angular contact ball bearings (often used in matched pairs), preload is especially critical.
At Beining Technology, we design and manufacture precision spindle bearings used in CNC machines worldwide. But we also share deep application knowledge—because the best bearing only delivers its full potential when paired with the right engineering support.
Need help choosing the right preload strategy for your spindle?
Contact our engineering team—we’ll help you get the accuracy, life, and reliability your machine deserves.
